(Go) Create a JWS Using ECDSA P-256 SHA-256

Creates and validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

Note: This example requires Chilkat v9.5.0.66 or greater.

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    // This requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // Note: This example requires Chilkat v9.5.0.66 or greater.

    // Use the following ECC key loaded from JWK format.
    sbJwk := chilkat.NewStringBuilder()
    sbJwk.Append("{\"kty\":\"EC\",")
    sbJwk.Append("\"crv\":\"P-256\",")
    sbJwk.Append("\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\",")
    sbJwk.Append("\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\",")
    sbJwk.Append("\"d\":\"jpsQnnGQmL-YBIffH1136cspYG6-0iY7X1fCE9-E9LI\"")
    sbJwk.Append("}")

    eccKey := chilkat.NewPrivateKey()
    // Note: This example loads the ECDSA key from JWK format.  Any format can be loaded
    // into the private key object. (See the online reference documentation..)
    success := eccKey.LoadJwk(*sbJwk.GetAsString())
    if success != true {
        fmt.Println(eccKey.LastErrorText())
        sbJwk.DisposeStringBuilder()
        eccKey.DisposePrivateKey()
        return
    }

    // Create the JWS Protected Header
    jwsProtHdr := chilkat.NewJsonObject()
    jwsProtHdr.AppendString("alg","ES256")

    jws := chilkat.NewJws()

    // Set the protected header:
    signatureIndex := 0
    jws.SetProtectedHeader(signatureIndex,jwsProtHdr)

    // Set the ECC key:
    jws.SetPrivateKey(signatureIndex,eccKey)

    // Set the payload.
    bIncludeBom := false
    payloadStr := "In our village, folks say God crumbles up the old moon into stars."
    jws.SetPayload(payloadStr,"utf-8",bIncludeBom)

    // Create the JWS
    // By default, the compact serialization is used.
    jwsCompact := jws.CreateJws()
    if jws.LastMethodSuccess() != true {
        fmt.Println(jws.LastErrorText())
        sbJwk.DisposeStringBuilder()
        eccKey.DisposePrivateKey()
        jwsProtHdr.DisposeJsonObject()
        jws.DisposeJws()
        return
    }

    fmt.Println("JWS: ", *jwsCompact)

    // Note: ECC signatures use random values, so the output will be different each time a signature is produced.
    // sample output:
    // JWS: eyJhbGciOiJFUzI1NiJ9.SW4gb3VyIHZpbGxhZ2UsIGZvbGtzIHNheSBHb2QgY3J1bWJsZXMgdXAgdGhlIG9sZCBtb29uIGludG8gc3RhcnMu.J6EGTNkeuEjehHHBu0SOKzifm8r35wbx49A5964pxzB7gannyZZPMkK7vmlaPJ-K8Xmm8cZsQySAPC12Xd8avw

    // Now load the JWS, validate, and recover the original text.
    jws2 := chilkat.NewJws()

    // Load the JWS.
    success = jws2.LoadJws(*jwsCompact)

    eccPubKey := eccKey.GetPublicKey()

    // Set the ECC public key used for validation.
    signatureIndex = 0
    jws2.SetPublicKey(signatureIndex,eccPubKey)
    eccPubKey.DisposePublicKey()

    // Validate the 1st (and only) signature at index 0..
    v := jws2.Validate(signatureIndex)
    if v < 0 {
        // Perhaps Chilkat was not unlocked or the trial expired..
        fmt.Println("Method call failed for some other reason.")
        fmt.Println(jws2.LastErrorText())
        sbJwk.DisposeStringBuilder()
        eccKey.DisposePrivateKey()
        jwsProtHdr.DisposeJsonObject()
        jws.DisposeJws()
        jws2.DisposeJws()
        return
    }

    if v == 0 {
        fmt.Println("Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both.")
        sbJwk.DisposeStringBuilder()
        eccKey.DisposePrivateKey()
        jwsProtHdr.DisposeJsonObject()
        jws.DisposeJws()
        jws2.DisposeJws()
        return
    }

    // If we get here, the signature was validated..
    fmt.Println("Signature validated.")

    // Recover the original content:
    fmt.Println(*jws2.GetPayload("utf-8"))

    // Examine the protected header:
    joseHeader := jws2.GetProtectedHeader(signatureIndex)
    if jws2.LastMethodSuccess() != true {
        fmt.Println("No protected header found at the given index.")
        sbJwk.DisposeStringBuilder()
        eccKey.DisposePrivateKey()
        jwsProtHdr.DisposeJsonObject()
        jws.DisposeJws()
        jws2.DisposeJws()
        return
    }

    joseHeader.SetEmitCompact(false)

    fmt.Println("Protected (JOSE) header:")
    fmt.Println(*joseHeader.Emit())
    joseHeader.DisposeJsonObject()

    // Output:

    // Signature validated.
    // In our village, folks say God crumbles up the old moon into stars.
    // Protected (JOSE) header:
    // { 
    //   "alg": "ES256"
    // }

    sbJwk.DisposeStringBuilder()
    eccKey.DisposePrivateKey()
    jwsProtHdr.DisposeJsonObject()
    jws.DisposeJws()
    jws2.DisposeJws()